Skull Radiographic Techniques Quiz

Skull Radiographic Techniques

• Skull radiographic techniques are essential for assessing specific conditions and referrals.
• The patient's condition should always be considered before proceeding with imaging.
• The patient is positioned supine with their head raised and immobilized on a non-opaque skull pad.
• The head is adjusted to ensure the median sagittal plane is perpendicular to the table/trolley, and the interpupillary line is perpendicular to the image receptor.
• The image receptor is positioned vertically against the lateral aspect of the head, parallel to the median sagittal plane, with its edge 5 cm above the vertex of the skull.
• The collimated horizontal beam is directed parallel to the interpupillary line, perpendicular to the median sagittal plane.
• The centring point is midway between the glabella and the external occipital protuberance, approximately 5 cm superior and posterior to the EAM.
• The long axis of the image receptor should be aligned with the long axis of the skull.
• The image should encompass all cranial bones and the 1st cervical vertebrae.
• A true lateral image results in superimposition of the lateral portions of the floors of the anterior and posterior cranial fossa.
• The clinoid processes of the sella turcica should also be superimposed.

Common Faults and Solutions

• Failure to include the occipital region may occur if the head is not adequately elevated using a pad.
• Poor superimposition of the lateral floors of the cranial fossa can be corrected by ensuring the interobital line is perpendicular to the cassette/receptor and the median sagittal plane is perpendicular to the trolley surface.

Skull Posterior-Anterior (PA) or Occipito-Frontal (OF) Projections

• Patient position: The patient sits facing the erect Bucky/receptor, with the median sagittal plane parallel to the Bucky/receptor and the interpupillary line perpendicular to the Bucky/receptor.
• The shoulders are rotated slightly to allow for correct positioning, and the patient may grip the Bucky inferiorly for stability.
• The image receptor is positioned transversely with its upper border 5 cm above the vertex of the skull.
• A radiolucent pad may be placed under the chin for support.
• The X-ray tube is centered to the Bucky/image receptor.
• The height of the Bucky/tube is adjusted for patient comfort.
• The collimated horizontal beam is centered midway between the glabella and the external occipital protuberance, approximately 5 cm superior and posterior to the EAM.

Occipito-Frontal (OF) Projections with Angulations

• Different degrees of beam angulation can be employed for OF projections, depending on departmental protocol and the anatomy to be visualized.
• The collimated horizontal beam is directed perpendicular to the Bucky/receptor along the median sagittal plane.
• Collimation should encompass the vertex of the skull superiorly, the region below the base of the occipital bone inferiorly, and the lateral skin margins.
• The tube is centered to the center of the Bucky receptor.
• For OF10°↓, OF15°↓, and OF20°↓ projections, a caudal angulation is applied, with the degree of angulation determined by the technique.
• The collimated horizontal beam is always centered to the center of the Bucky/image receptor after the tube angulation is applied.

Essential Image Characteristics for OF Projections

• All cranial bones, including skin margins, should be within the image.
• The skull should not be rotated.
• The degree of beam angulation is evaluated by assessing the position of the petrous ridges within the orbits.
• In a true OF projection, the petrous ridges are completely superimposed within the orbit, with their upper borders coincident with the upper 1/3 of the orbit.
• In an OF10°↓ projection, the petrous ridges appear in the middle 1/3 of the orbit.
• In an OF15°↓ projection, the petrous ridges appear in the lower 1/3 of the orbit.
• In an OF20°↓ projection, the petrous ridges appear just below the inferior orbital margin.

Fronto-Occipital (FO) Projections

• FO projections demonstrate the same anatomy as OF projections, but the orbits and frontal bone are magnified due to their position further from the image receptor.
• FO projections are typically used when the patient cannot be moved and must be imaged supine.
• These projections increase radiation dose to the orbits and may cause some loss of resolution of anterior skull structures.

Patient Positioning for FO Projections

• The patient lies supine with the posterior aspect of the skull resting on the image receptor/gridded CR cassette.
• The head is adjusted to ensure the median sagittal plane is perpendicular to the image receptor and coincident with its midline.
• The EAMs should be equidistant from the image receptor to minimize rotation.
• The orbito-meatal baseline is perpendicular to the image receptor.

X-ray Beam Direction and Location for FO Projection

• All angulations for FO projections are made cranially.
• The collimated vertical X-ray beam is directed perpendicular to the image receptor along the median sagittal plane.
• Collimation should include the vertex of the skull superiorly, the base of the occipital bone inferiorly, and the lateral skin margins.
• For FO10°↑, FO15°↑, and FO20°↑ projections, a cranial angulation is applied, with the degree of angulation determined by the projection required.
• The image receptor is displaced superiorly to allow for the tube angulation.

Townes Projection

• Patient positioning: The patient lies supine with the posterior aspect of the skull resting on the image receptor/gridded CR cassette.
• The head is adjusted to ensure the median sagittal plane is perpendicular to the image receptor and coincident with its midline.
• The orbito-meatal baseline should be perpendicular to the image receptor.
• The central ray is angled caudally at 30 degrees to the orbito-meatal plane.
• Centering is in the midline, with the beam passing midway between the external auditory meatuses, approximately 5 cm above the glabella.
• The top of the cassette is positioned adjacent to the vertex of the skull to prevent the area of interest from being projected off the bottom of the image.

Essential Image Characteristics for Townes Projection

• The sella turcica of the sphenoid bone is projected within the foramen magnum.
• The image should include all of the occipital bone and the posterior parts of the parietal bone.
• The lambdoidal suture should be clearly visualized.
• The skull should not be rotated, which can be assessed by ensuring the sella turcica appears centrally in the foramen magnum.

Submento-Vertex (SMV) Projection

• Patient positioning: The patient can be imaged erect or supine.
• A supine technique is advised if the patient is unsteady.
• In the supine position, the patient's shoulders are raised, and the neck is hyperextended to bring the vertex of the skull in contact with the image receptor/gridded CR cassette.
• The head is adjusted to ensure the EAMs are equidistant from the image receptor.
• The median sagittal plane is perpendicular to the image receptor, aligned with its midline.
• The orbito-meatal plane is as near as possible parallel to the image receptor.
• In the erect position, the patient sits facing the X-ray tube, a short distance away from the vertical Bucky/receptor.
• Neck hyperextension allows the head to fall back until the vertex of the skull makes contact with the center of the vertical image receptor.
• The remaining positioning is as described for the supine technique.

X-ray Beam Direction and Location for SMV Projection

• The central ray is directed perpendicular to the orbito-meatal plane.
• Centering is midway between the external auditory meatuses.

Essential Image Characteristics for SMV Projection

• An optimal projection will demonstrate the mandibular angles clear of the petrous portions of the temporal bone.
• The foramina of the middle cranial fossa should be seen symmetrically either side of the midline.

Optic Canal Projection

• The optic canal opens posteriorly within the bony orbit at the optic foramen.
• The canal passes forwards and laterally at approximately 35° to the median sagittal plane and downwards at approximately 35° to the orbito-meatal plane.
• This is the path the central ray must follow to demonstrate the foramen for imaging.
• Both sides are usually imaged separately for comparison.

Patient Positioning for Optic Canal Projection

• The patient sits erect with the nose, cheek, and chin of the side being examined in contact with the Bucky/image receptor.
• The center of the orbit of the side under examination should coincide with the center of the image receptor.
• The median sagittal plane is adjusted to make an angle of 35° to the vertical.
• The orbito-meatal baseline is raised 35° from the horizontal.

X-ray Beam Direction and Location for Optic Canal Projection

• The collimated horizontal central ray is centered to the middle of the image receptor.
• This is to a point 7.5 cm superior and 7.5 cm posterior to the uppermost EAM, ensuring the central ray emerges from the center of the orbit and contacts the image receptor.
• A side marker may be placed above the superior orbital margin.